By Juliet Eilperin
Washington Post Staff Writer
Wednesday, January 19, 2005; Page A17

In his worn navy windbreaker, 63-year-old climatologist James E. Hansen looks more like the Iowa farm native that he is than a rebel -- but he's both.

Hansen, a lifelong government employee who heads NASA's Goddard Institute for Space Studies in New York, has inspired both anger and awe in the nation's scientific and political communities since publicly denouncing the Bush administration's policy on climate change last year.

Speaking in the swing state of Iowa days before the presidential election, Hansen accused a senior administration official of trying to block him from discussing the dangerous effects of global warming.

In the University of Iowa speech, Hansen recounted how NASA Administrator Sean O'Keefe told him in a 2003 meeting that he shouldn't talk "about dangerous anthropogenic interference" -- humans' influence on the atmosphere -- "because we do not know enough or have enough evidence for what would constitute dangerous anthropogenic interference."

But Hansen said that scientists know enough to conclude we have reached this danger point and that their efforts to get the word out are being blocked by the administration. "In my more than three decades in government, I have never seen anything approaching the degree to which information flow from scientists to the public has been screened and controlled as it has now," Hansen said. He added that although the administration wants to wait 10 years to evaluate climate change, "delay of another decade, I argue, is a colossal risk."

Senior administration officials deny Hansen's charges: O'Keefe spokesman Glenn Mahone said the administrator doesn't "recall ever having the conversation" on climate change that Hansen described, adding that O'Keefe "has encouraged open dialogue and open conversation about those issues."

But Hansen, who has worked for NASA since he was 25, has continued to chide the administration for not moving swiftly enough to address global warming. In a recent interview, he called Bush officials "reasonable people" who need to be convinced that climate change is an urgent matter.

"As the evidence gathers, you would hope they would be flexible," Hansen said in the slow, measured tones he has retained from his years growing up on an Iowa farm. "We have to deal with this. You can't ignore it."

The ongoing sparring match between Hansen and his superiors underscores a broader tension between President Bush's top policy advisers and many senior U.S. scientists, who have loudly blasted the administration's approach to environmental questions in recent months. Nearly 50 Nobel laureates endorsed Sen. John F. Kerry (D-Mass.) for president; this year the Union of Concerned Scientists has collected more than 6,000 scientists' signatures on a letter questioning how the president applies research to policymaking.

After the barrage of criticism, John H. Marburger III, Bush's top science adviser, told Science magazine that if the researchers continue their protests, they might alienate influential lawmakers who set federal science budgets.

Hansen, who also took on Bush's father, President George H.W. Bush, on the question of climate change in the late 1980s, is undeterred. An advocate for caps on carbon dioxide emissions and stricter fuel standards for automobiles -- two policies that Bush advisers say would hurt the U.S. economy -- Hansen said he has to oppose what he said is the government's choice to delay action on new regulations to limit emissions under the guise of seeking more scientific research.

"We have got to be an independent voice. We should not be influenced in any way by funding," Hansen said.

Hansen is no stranger to controversy. In 1989, he accused the Office of Management and Budget of watering down his congressional testimony on climate change to make the situation appear less dire.

"I'm strictly trying to understand the Earth as a planet," said Hansen, who started his career studying the clouds around Venus but switched in 1978 to climate modeling.

The administration has done nothing to punish Hansen since he made his public comments last fall, and Marburger said in an interview that he considers Hansen "a very good climate scientist" who should stick to scientific analysis instead of policy prescriptions.

"I take his work seriously. His work has had a big impact on this administration's climate-change policy," Marburger said. "But he's not an economist. The fact that he's a good scientist does not necessarily make him the best person to formulate policy that would affect the economy."

Former vice president Al Gore, who backs limits on emissions of carbon dioxide, said the administration's strained relationship with Hansen shows the "contempt for the rule of reason" of Bush and his deputies.

"When science conflicts with the exercise of power, they attempt to demean the messenger attempting to deliver the truth, and they seek out self-interested advocates of alternative views of reality," said Gore, who as a senator defended Hansen during the controversy over his 1989 testimony.

Within the scientific community, Hansen remains respected for much of his research, though some have questioned his recent studies on the effect of aerosols on global warming. He is popular at the space institute -- housed at Columbia University above the famed diner from the comedy series "Seinfield" -- where he has played Frisbee in the halls.

Gavin A. Schmidt, a climatologist who has worked with Hansen at Goddard for nearly a decade, said Hansen gets his leverage from the fact that he a senior scholar who is still breaking scientific ground.

"Very few people have that kind of longevity and credibility and are still doing new things," Schmidt said. "Any time he says something, it's news. He still sets the agenda."

Kevin E. Trenberth, who heads the climate analysis section of the nonprofit, federally funded National Center for Atmospheric Research, said Hansen's willingness to espouse the dominant scientific view on climate change "is a responsible thing to do, even if it puts at potential jeopardy his own position." Trenberth added: "This is an important issue, a long-term issue that affects humanity in the future."

Some, however, have questioned Hansen's approach. Patrick J. Michaels, a climatologist and a senior fellow in environmental studies at the libertarian Cato Institute, said it was inappropriate for Hansen as a federal employee to attack the administration in a battleground state less than two weeks before the election.

"The problem with Jim is he does climate and then he makes policy decisions that I don't think are very thoughtful," said Michaels, who receives funding from public and industry sources, and opposes mandatory carbon controls.

Hansen has found some common ground with administration officials, who like his recent findings that curbing methane emissions from landfills, mining operations and gas-drilling ventures can help counter warming. The administration recently persuaded more than a dozen countries to sign a pact to capture methane before it is released into the atmosphere, a program Hansen praised.

But it remains unclear whether Bush officials can reach some sort of detente with Hansen, who said in a recent e-mail that he is not interested in "making the administration mad" but in persuading it to cut carbon dioxide emissions from power plants and elsewhere. But in the meantime, Hansen said he will continue to press ahead with both research and advocacy.

"You can't just give up," he said. "I remain optimistic, even in this administration, that the evidence is going to become strong enough so there's a chance there will be a change in policy."